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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Impact of microwave derived soil moisture on hydrologic simulations using a spatially distributed water balance model

Spatial distributions of soil moisture over an agricultural watershed with a drainage area of 60 ha were derived from two NASA microwave remote sensors, and then used as a feedback to determine the initial condition for a distributed water balance model. Simulated hydrologic fluxes over a period of twelve days were compared with field observations and with model predictions based on a streamflow derived initial condition. The results indicated that even the low resolution remotely sensed data can improve the hydrologic model's performance in simulating the dynamics of unsaturated zone soil moisture. For the particular watershed under study, the simulated water budget was not sensitive to the resolutions of the microwave sensors.

Lin, D. S.↗
DOE OSTI2022

An Efficient Time-Domain Model to Simulate Parametric Resonances in a Floating Body Free to Move in Six Degrees of Freedom: Preprint

We present a computationally efficient time-domain model capable of simulating parametric resonances in a floating body in waves. The model assumes all wave forces to be linear, but the inertia and restoring forces acting on the body are expanded to second order in body motions. The simulation speed on a standard computer is approximately 40 times faster than real time. The model is applied to a soft-moored floating axisymmetric body which absorbs energy through heave, but is otherwise free to move in six degrees of freedom. Under certain conditions, we show that the body responds parametrically with large amplitudes not only in surge and pitch, but also in sway, roll, and yaw, provided it is given some small initial displacement in one of these out-of-plane modes. The predictions are confirmed by simulations using state-of-the-art nonlinear Froude-Krylov and computational fluid dynamics models.

parametric resonance↗
DOE OSTI2015

A hybrid model for simulation of secondary electron emission in plasma immersion ion implantation under different pulse rise time

A hybrid fluid Particle in Cell–Monte Carlo Collision (PiC–MCC) model is presented to study the effect of secondary electron emission on the plasma immersion ion implantation process under different pulse rise time. The model describes the temporal evolution of various parameters of plasma such as ion density, ion velocity, secondary electron density, and secondary electron current for different rise times. A 3D–3 V PiC–MCC model is developed to simulate the secondary electrons which are emitted from the sample surface while the plasma ions and electrons are treated using a 1D fluid model. The simulation results indicate that the secondary electron density and secondary electron current increase as the rise time decreases. The main differences between the results for different rise times are found during the initial phase of the pulse. The results are explained through studying the fundamental parameters of plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Generation of Reversible C++ Code for Optimistic Parallel Discrete Event Simulation

The reversible execution of C/C++ code has been a target of research and engineering for more than a decade as reversible computation has become a central notion in large-scale parallel discrete event simulation (PDES). The simulation models that are implemented for PDES are of increasing complexity and size and require various language features to support abstraction, encapsulation, and composition when building a simulation model. In this paper, we focus on parallel simulation models that are written with user-defined C++ abstractions and abstractions of the C++ Standard Library. We present an approach based on incremental state saving for establishing reversibility of C++ and an evaluation for a kinetic Monte-Carlo simulation implemented in C++. Although a significant runtime overhead is introduced with our technique, it is an enormous win that it allows using the entire C++ language, and has that code automatically transformed into reversible code to enable parallel execution with the Rensselaer’s optimistic simulation system (ROSS).

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1994

Piloted Evaluation of an Integrated Methodology for Propulsion and Airframe Control Design

An integrated methodology for propulsion and airframe control has been developed and evaluated for a Short Take-Off Vertical Landing (STOVL) aircraft using a fixed base flight simulator at NASA Lewis Research Center. For this evaluation the flight simulator is configured for transition flight using a STOVL aircraft model, a full nonlinear turbofan engine model, simulated cockpit and displays, and pilot effectors. The paper provides a brief description of the simulation models, the flight simulation environment, the displays and symbology, the integrated control design, and the piloted tasks used for control design evaluation. In the simulation, the pilots successfully completed typical transition phase tasks such as combined constant deceleration with flight path tracking, and constant acceleration wave-off maneuvers. The pilot comments of the integrated system performance and the display symbology are discussed and analyzed to identify potential areas of improvement.

Bright, Michelle M.↗
DOE OSTI2022

A New Model for Simulating the Imbibition of a Wetting-Phase Fluid in a Matrix-Fracture Dual Connectivity System

The imbibition experiment is an effective approach for measuring petrophysical properties of porous media, with many such experiments performed over the past decade. Quite some empirical, analytical, and numerical models have been developed to simulate spontaneous imbibition of the wetting phase fluid into porous media, but limitations still exist. In previous studies, the imbibition process has been considered to give a piston-like displacement or the porous medium modeled as multiply-sized pores linked with bonds; both approaches fail to yield comprehensive results due to their neglect of the presence of irregular fractures or nonuniform flow paths through the matrix. By building a numerical model for simulating laboratory-scale experimental data, we performed imbibition tests on several fractured Barnett Shale samples having fractures either parallel ( P ) or transverse ( T ) to the bedding plane and used MATLAB to build a new numerical model by combining the imbibition process in fractures and the matrix using concepts from percolation theory. The experimental data show that the rocks with P -direction fractures have a more steady increase of imbibition rates than the case of T -direction one. As the shale matrix with low pore connectivity hampers the upward water movement, the imbibition rate of shales with T -direction fractures will decrease suddenly after the bottom layer in contact with water is saturated during the initial period. This wetting phase movement (WPM) model can simulate 3D porous media with 2D fractures. The rate of imbibition by fractured porous media is associated with physical parameters such as porosity and fracture distribution (e.g., the number and angle of fractures). Using Monte Carlo methods, we examined fracture parameters and predicted elapsed time and cumulative water imbibition, for the Barnett Shale samples. The results show that the rate of imbibed water mass is sensitive to the number of fractures directly connected to water source, and the connectivity between two neighboring grid cells is a key parameter for the wetting-front progression. The findings of this study can help to better understand the imbibition process with multiple influencing processes and factors in fractured-matrix rocks. Although the experiments, data simulation, and prediction results are based only on Barnett Shale samples, the model is readily applicable to imbibition tests of other fractured rocks to show the spatial and temporal behavior during a dynamic imbibition process that are not easily captured experimentally.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

A calibration procedure to improve global rice yield simulations with EPIC

Crop models are increasingly used to assess impacts of climate change/variability and management practices on productivity and environmental performance of alternative cropping systems. Calibration is an important procedure to improve reliability of model simulations, especially for large area applications. However, global-scale crop model calibration has rarely been exercised due to limited data availability and expensive computing cost. Here we present a simple approach to calibrate Environmental Policy Integrated Climate (EPIC) model for a global implementation of rice. We identify four parameters (potential heat unit – PHU, planting density – PD, harvest index – HI, and biomass energy ratio – BER) and calibrate them regionally to capture the spatial pattern of reported rice yield in 2000. Model performance is assessed by comparing simulated outputs with independent FAO national data. The comparison demonstrates that the global calibration scheme performs satisfactorily in reproducing the spatial pattern of rice yield, particularly in main rice production areas. Spatial agreement increases substantially when more parameters are selected and calibrated, but with varying efficiencies. Among the parameters, PHU and HI exhibit the highest efficiencies in increasing the spatial agreement. Simulations with different calibration strategies generate a pronounced discrepancy of 5–35% in mean yields across latitude bands, and a small to moderate difference in estimated yield variability and yield changing trend for the period of 1981–2000. Present calibration has little effects in improving simulated yield variability and trends at both regional and global levels, suggesting further works are needed to reproduce temporal variability of reported yields. This study highlights the importance of crop models’ calibration, and presents the possibility of a transparent and consistent up scaling approach for global crop simulations given current availability of global databases of weather, soil, crop calendar, fertilizer and irrigation management information, and reported yield.

Crop model↗
NASA NTRS1984

System analysis for the Huntsville Operational Support Center distributed computer system

The Huntsville Operations Support Center (HOSC) is a distributed computer system used to provide real time data acquisition, analysis and display during NASA space missions and to perform simulation and study activities during non-mission times. The primary purpose is to provide a HOSC system simulation model that is used to investigate the effects of various HOSC system configurations. Such a model would be valuable in planning the future growth of HOSC and in ascertaining the effects of data rate variations, update table broadcasting and smart display terminal data requirements on the HOSC HYPERchannel network system. A simulation model was developed in PASCAL and results of the simulation model for various system configuraions were obtained. A tutorial of the model is presented and the results of simulation runs are presented. Some very high data rate situations were simulated to observe the effects of the HYPERchannel switch over from contention to priority mode under high channel loading.

Ingels, F. M.↗
NASA NTRS1998

The NASA-Langley Wake Vortex Modelling Effort in Support of an Operational Aircraft Spacing System

Two numerical modelling efforts, one using a large eddy simulation model and the other a numerical weather prediction model, are underway in support of NASA's Terminal Area Productivity program. The large-eddy simulation model (LES) has a meteorological framework and permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, humidity, and atmospheric turbulence. Results from the numerical simulations are being used to assist in the development of algorithms for an operational wake-vortex aircraft spacing system. A mesoscale weather forecast model is being adapted for providing operational forecast of winds, temperature, and turbulence parameters to be used in the terminal area. This paper describes the goals and modelling approach, as well as achievements obtained to date. Simulation results will be presented from the LES model for both two and three dimensions. The 2-D model is found to be generally valid for studying wake vortex transport, while the 3-D approach is necessary for realistic treatment of decay via interaction of wake vortices and atmospheric boundary layer turbulence. Meteorology is shown to have an important affect on vortex transport and decay. Presented are results showing that wake vortex transport is unaffected by uniform fog or rain, but wake vortex transport can be strongly affected by nonlinear vertical change in the ambient crosswind. Both simulation and observations show that atmospheric vortices decay from the outside with minimal expansion of the core. Vortex decay and the onset three-dimensional instabilities are found to be enhanced by the presence of ambient turbulence.

Proctor, Fred H.↗
NASA NTRS2009

NASA Standard for Models and Simulations: Credibility Assessment Scale

As one of its many responses to the 2003 Space Shuttle Columbia accident, NASA decided to develop a formal standard for models and simulations (M&S). Work commenced in May 2005. An interim version was issued in late 2006. This interim version underwent considerable revision following an extensive Agency-wide review in 2007 along with some additional revisions as a result of the review by the NASA Engineering Management Board (EMB) in the first half of 2008. Issuance of the revised, permanent version, hereafter referred to as the M&S Standard or just the Standard, occurred in July 2008. Bertch, Zang and Steeleiv provided a summary review of the development process of this standard up through the start of the review by the EMB. A thorough recount of the entire development process, major issues, key decisions, and all review processes are available in Ref. v. This is the second of a pair of papers providing a summary of the final version of the Standard. Its focus is the Credibility Assessment Scale, a key feature of the Standard, including an example of its application to a real-world M&S problem for the James Webb Space Telescope. The companion paper summarizes the overall philosophy of the Standard and an overview of the requirements. Verbatim quotes from the Standard are integrated into the text of this paper, and are indicated by quotation marks.

Babula, Maria↗
DOE OSTI2017

Reduced ENSO variability at the LGM revealed by an isotope‐enabled Earth system model

Abstract Studying the El Niño–Southern Oscillation (ENSO) in the past can help us better understand its dynamics and improve its future projections. However, both paleoclimate reconstructions and model simulations of ENSO strength at the Last Glacial Maximum (LGM; 21 ka B.P.) have led to contradicting results. Here we perform model simulations using the recently developed water isotope‐enabled Community Earth System Model (iCESM). For the first time, model‐simulated oxygen isotopes are directly compared with those from ENSO reconstructions using the individual foraminifera analysis (IFA). We find that the LGM ENSO is most likely weaker comparing with the preindustrial. The iCESM suggests that total variance of the IFA records may only reflect changes in the annual cycle instead of ENSO variability as previously assumed. Furthermore, the interpretation of subsurface IFA records can be substantially complicated by the habitat depth of thermocline‐dwelling foraminifera and their vertical migration with a temporally varying thermocline.

Zhu, Jiang↗
DOE OSTI2014

Thread Group Multithreading: Accelerating the Computation of an Agent-Based Power System Modeling and Simulation Tool -- C GridLAB-D

GridLAB-DTM is an open source next generation agent-based smart-grid simulator that provides unprecedented capability to model the performance of smart grid technologies. Over the past few years, GridLAB-D has been used to conduct important analyses of smart grid concepts, but it is still quite limited by its computational performance. In order to break through the performance bottleneck to meet the need for large scale power grid simulations, we develop a thread group mechanism to implement highly granular multithreaded computation in GridLAB-D. We achieve close to linear speedups on multithreading version compared against the single-thread version of the same code running on general purpose multi-core commodity for a benchmark simple house model. The performance of the multithreading code shows favorable scalability properties and resource utilization, and much shorter execution time for large-scale power grid simulations.

Jin, Shuangshuang↗
NASA NTRS2015

Assessing Disparities of Dengue Virus Transmission Risk across the US-Mexican Border Using a Climate Driven Vector-Epidemiological Model

Dengue fever is a mosquito‐borne viral disease reemerging throughout much of the tropical Americas. Dengue virus transmission is explicitly influenced by climate and the environment through its primary vector, Aedes aegypti. Temperature regulates Ae. aegypti development, survival, and replication rates as well as the incubation period of the virus within the mosquito. Precipitation provides water for many of the preferred breeding habitats of the mosquito, including buckets, old tires, and other places water can collect. Although transmission regularly occurs along the border region in Mexico, dengue virus transmission in bordering Arizona has not occurred. Using NASA's TRMM (Tropical Rainfall Measuring Mission) satellite for precipitation input and Daymet for temperature and supplemental precipitation input, we modeled dengue transmission along a US‐Mexico transect using a dynamic dengue transmission model that includes interacting vector ecology and epidemiological components. Model runs were performed for 5 cities in Sonora, Mexico and southern Arizona. Employing a Monte Carlo approach, we performed ensembles of several thousands of model simulations in order to resolve the model uncertainty arising from using different combinations of parameter values that are not well known. For cities with reported dengue case data, the top model simulations that best reproduced dengue case numbers were retained and their parameter values were extracted for comparison. These parameter values were used to run simulations in areas where dengue virus transmission does not occur or where dengue fever case data was unavailable. Additional model runs were performed to reveal how changes in climate or parameter values could alter transmission risk along the transect. The relative influence of climate variability and model parameters on dengue virus transmission is assessed to help public health workers prepare location specific infection prevention strategies.

Morin, Cory↗
DOE OSTI2019

CHARMM-GUI Glycan Modeler for modeling and simulation of carbohydrates and glycoconjugates

Characterizing glycans and glycoconjugates in the context of three-dimensional structures is important in understanding their biological roles and developing efficient therapeutic agents. Computational modeling and molecular simulation have become an essential tool complementary to experimental methods. In this work, we present a computational tool, Glycan Modeler for in silico N–/O –glycosylation of the target protein and generation of carbohydrate-only systems. In our previous study, we developed Glycan Reader , a web-based tool for detecting carbohydrate molecules from a PDB structure and generation of simulation system and input files. As integrated into Glycan Reader in CHARMM-GUI, Glycan Modeler (Glycan Reader & Modeler) enables to generate the structures of glycans and glycoconjugates for given glycan sequences and glycosylation sites using PDB glycan template structures from Glycan Fragment Database (http://glycanstructure.org/fragment-db). Our benchmark tests demonstrate the universal applicability of Glycan Reader & Modeler to various glycan sequences and target proteins. We also investigated the structural properties of modeled glycan structures by running 2-μs molecular dynamics simulations of HIV envelope protein. The simulations show that the modeled glycan structures built by Glycan Reader & Modeler have the similar structural features compared to the ones solved by X-ray crystallography. We also describe the representative examples of glycoconjugate modeling with video demos to illustrate the practical applications of Glycan Reader & Modeler . Glycan Reader & Modeler is freely available at http://charmm-gui.org/input/glycan.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Development of an Advanced Simulator to Model Mobility Control and Geomechanics during CO 2 Floods

The simulator is an isothermal, three-dimensional, four-phase, compositional, equation-of–state (EOS) simulator. We have named the simulator UTDOE-CO2 capable of simulating various recovery processes (i.e., primary, secondary waterflooding, and miscible and immiscible gas flooding). We include both the Peng-Robinson EOS and the Redlich-Kwong EOS models. A Gibbs stability test is also included in the model to perform a phase identification test to consistently label each phase for subsequent property calculations such as relative permeability, viscosity, density, interfacial tension, and capillary pressure. Our time step strategy is based on an IMPEC-type method (implicit pressure and explicit concentration). The gridblock pressure is solved first using the explicit dating of saturation-dependent terms. Subsequently, the material balance equations are solved explicitly for the total concentration of each component. The physical dispersion term is also included in the governing equations. The simulator includes (1) several foam model(s) for gas mobility control, (2) compositional relative permeability models with the hysteresis option, (3) corner point grid and several efficient solvers, (4) geomechanics module to compute stress field as the result of CO 2 injection/production, (5) the format of commercial visualization software, S3graf from Science-soft Ltd., was implemented for user friendly visualization of the simulation results. All tasks are completed and the simulator was fully tested and delivered to the DOE office including a user’s guide and several input files and the executable for Windows Pcs. We have published several SPE papers, presented several posters, and one MS thesis is completed (V. Pudugramam, 2013) resulting from this DOE funded project.

02 PETROLEUM↗
DOE OSTI2015

Prototyping and validating requirements of radiation and nuclear emergency plan simulator

Organizational incapability in developing unrealistic, impractical, inadequate and ambiguous mechanisms of radiological and nuclear emergency preparedness and response plan (EPR) causing emergency plan disorder and severe disasters. These situations resulting from 65.6% of poor definition and unidentified roles and duties of the disaster coordinator. Those unexpected conditions brought huge aftermath to the first responders, operators, workers, patients and community at large. Hence, in this report, we discuss prototyping and validating of Malaysia radiation and nuclear emergency preparedness and response plan simulation model (EPRM). A prototyping technique was required to formalize the simulation model requirements. Prototyping as systems requirements validation was carried on to endorse the correctness of the model itself against the stakeholder’s intensions in resolving those organizational incapability. We have made assumptions for the proposed emergency preparedness and response model (EPRM) through the simulation software. Those assumptions provided a twofold of expected mechanisms, planning and handling of the respective emergency plan as well as in bringing off the hazard involved. This model called RANEPF (Radiation and Nuclear Emergency Planning Framework) simulator demonstrated the training emergency response perquisites rather than the intervention principles alone. The demonstrations involved the determination of the casualties’ absorbed dose range screening and the coordination of the capacity planning of the expected trauma triage. Through user-centred design and sociotechnical approach, RANEPF simulator was strategized and simplified, though certainly it is equally complex.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗